1. Field of the Invention
The invention relates to an alignment apparatus and, more particularly, to an alignment optical system of a projection type exposing apparatus to manufacture a semiconductor device.
2. Related Background Art
The alignment optical system of such a kind of conventional alignment apparatus has a construction as shown in FIG. 5. That is, a microscope objective section 1 to detect images of marks X.sub.1 and Y.sub.1 is arranged at the position corresponding to an area on a mask (reticle) 17 in which alignment marks X.sub.1 and Y.sub.1 are arranged. The images of the alignment marks X.sub.1 and Y.sub.1 detected by the objective section 1 are respectively projected to an X-axis detecting section 4 and a Y-axis detecting section 6 each of which is constructed by a photodetector or the like through the alignment optical system including an optical path divider such as a half mirror 3 and the like (only the half mirror 3 is shown in the diagram).
The X-axis and Y-axis detecting sections 4 and 6 have slits 5 and 7 of the shapes which substantially coincide with the shapes of the alignment marks X.sub.1 and Y.sub.1. The reticle 17 is aligned by setting the alignment mark X.sub.1 and slit 5 into a predetermined positional relation and by setting the alignment mark Y.sub.1 and slit 7 into a predetermined positional relation. With respect to the other alignment marks X.sub.2 and Y.sub.2 on the reticle as well, the images detected by a microscope objective section 8 are respectively projected to an X-axis detecting section 11 and a Y-axis detecting section 13 and the alignment marks X.sub.2 and Y.sub.2 and the slits 12 and 14 are set into predetermined positional relations, thereby aligning the reticle in a manner similar to the above method.
In U.S. Pat. No. 4,710,029, there is disclosed a method whereby reference marks formed on a stage onto which a wafer is put are used, one of the slits in the alignment optical system and the reference mark are made coincide through a projection objective lens, and the stage is moved after that, thereby adjusting the alignment optical system so that the reference mark and other slits in the alignment optical system coincide through the projection objective lens. Particularly, there is disclosed an apparatus for optically correcting a rotational error of the alignment optical system for the moving direction of the stage due to a fluctuation of a projection magnification.
In recent years, however, there is a tendency such that a chip area of semiconductor device is more and more increasing. An enlargement of an exposure area which is needed on the reticle is required. In association with the enlargement of the exposure area, it is necessary to change the arrangement of the alignment marks on the reticle. In accordance with the manufacturing steps of the semiconductor device, there is also a case where a plurality of kinds of exposure areas of the reticles are used for one apparatus. Each time the kind of reticle is changed, the arrangement of the alignment marks differs.
In the conventional apparatus with the construction as mentioned above, however, since the alignment optical system is fixed to the apparatus, the use of the reticles with different exposure areas (namely, the positions of the alignment marks are different) is limited.
An alignment apparatus of a construction such that (a whole or a part of) the alignment optical system is made movable has been disclosed in U.S. Pat. No. 4,402,596 or 4,636,626. A method of optically correcting a mechanical position deviation in association with the movement of the alignment optical system has been disclosed in U.S. Pat. No. 4,636,626.
However, a method of detecting the positional relations among a plurality of alignment optical systems through the projection objective lens is not disclosed in U.S. Pat. Nos. 4,402,596 and 4,636,626. The positional relations among a plurality of alignment optical systems cannot be changed and set to predetermined values.